<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="lib/jquery-3.3.1.js"></script>
    <style>
       .current{
           color: skyblue;
       }
    </style>
</head>
<body>
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
    </ul>
    <div>div</div>
    <button>btn</button>
    <script>
    /* 
    addClass
    removeClass
    toggleClass  -->触发器
    */
    $("li").click(function(){
         $(this).addClass("current").siblings().removeClass("current")
    })
    $("button").click(function(){
        $("div").toggleClass("current");
    })
    </script>
</body>
</html>